Motor control system



Dec. 26, 1944. T, MONTGOMERY 2,366,148

MOTOR CONTROL SYSTEM Filed April 18, 1941 Patented Dec. 26, 1944 UNITEDSTATESl PATENT OFFICE Moron CONTROL SYSTEM Teri-yl B. Montgomery,Wauwatosa, Wis., assignor to Allis-Chalmers Manufacturing Company,Milwaukee, Wis., a corporation of Delaware Application April 18, 1941,Serial No. 389,156

13 Claims.

This invention relates in general to a motor control system and relatesparticularly to a control system for a motor controlling the tensionmotor changes abnormally during periods of ac-V celeration anddeceleration and therefore attempt-,s were made to modify or compensatethe controlling mechanism during' such periods` in order to maintain thedesired tension.

Inaccuracies in the prior art tensioning systems, during periods ofacceleration and deceleration, were occasioned by the fact that themodiilcation or compensation of the controlling mechanism during periodsof acceleration and deceleration was made entirely independent of thewidth of the strip of material being tensioned and entirely independentof the amount of strip material on the reel at the particular time ofthe acceleration or deceleration. In other Words, the compensationduring acceleration and deceln eration was not truly dependent upon theinertie, of lhe strip material on the reel.

In control systems of the prior art, in which a strip of material islosing Wound; on or unn wound from a reel, a tension has losen appliedto the strip of material by controlling the power output the reel motor.For constant tension, the por er output ci the reel motor mainte'u f'ant value, for given strip speed, indeL1 do lr change in the speed oi'the due to lauld=ufo or h-uildndown s material on the rcel.

Qontrol of the power output of the reel motor has been obtained hyacircuit controller responla sive 'to the differential between voltagesof small generators mechanically connected to the roll and reel motors.These prior art control sysm tems di@ not provide for compensation ofthe controlling element so that the tensionin the strip would hemaintained at the desired value during acceleration and deceleration. Inthese upon the commutators thereof, the resistance of which would varygreatly under no load conditions. thereby giving an incorrect referencevolt-,- age.

It is therefore an object of the present invention to provide a controlsystem of the above type which will avoid any or al1 of the abovedisadvantages.

It is also an object of the present invention to provide acontrol/system for a m tor utilized in tensioning a strip of material,in W, ich the modiflcation or compensation of the control mechanism'during periods of acceleration or deceleration of the motor isIcorrected either in accord ance with. the Width of the particular stripbeing tensioned or in accordance with the amount of such strip woundupon the reel at the particular time of the acceleration or decelerationor in accordance with both such conditions.

It is also an object of the present invention to provide a striptensioning control system utilizing small direct current generators inwhich inaccuracies occasioned by differing saturation curves of thegenerators and hy the no load characteristics thereof are avoided.

@Meets and advantages other than thoseahove set forth will ce apparentfrom the following description when read in connection with theaccompanying' drawing, in which' Fig. l a schematic diagram ofconnections oi o control system embodying the present invention hotlineof curves risolti in detern oi the resistance ized Sor on in controlsharm.

nicolliterl force. a part shown in l tension control system shown 1includes two motors l t a generator it, the voltage of e varledhy therheostat to vary' the d. oi? c, strip A hoostereenerator lli tu circuitwith the reel motor l is regulated to maintain the current in the reelmotor cire cuit at a constant value. The field 2t of the reel motor 'iis varied to maintain the power delivered by motor 1 to the reel 6 inaccordance with a predetermined sequence of values, thereby maintainingthe desired tension on the strip B. Normally, that'is, at a constantspeed of the strip 5, the value of the power transmitted be tween reel Band the machine l is constant.

The booster regulator II is compensated durlng periods of accelerationand deceleration of the reel motor 1 to add to or subtract from thecurrent in the reel motor 1 in order to maintain the desired striptension during such acceleration and deceleration. This compensation iseffected by a coil 22 on the regulator I3, the eect of which is added toor subtracted from that of the regulator main coil 23, only duringperiods of acceleration or deceleration, by relays 5l' or 5S. @ne or theother of these relays is energized by closure switch 58 or switch SOwhich at the same time causes energzation ci of the main mill speedrheostat glzation field 4 wh" i the generator it to v "ation provided byd through a predetermined part of one of a baul: oi resistances 26 to30, variously.r in

eluded in circuit with coil 22. Determination oi the particularresistance used at any time is ccntrolled by the rheostat 2i inaccordance with the amount of material wound on the reel S.feterinination of the particular part of such resistance is controlledby the setting of rheostat 25 in accordance the width of the strip 5.

f`ziecically, the strip of material i is shown as being wound Lnwoundfrom a reel 6 and passing around rolls t, which may perform a reducing,nishing, tensioning or similar operation on the strip. The motors 1 and3 are energized from a generator ill which is shown as driven by analternating curre motor il. A booster generator i2 is connecte in thearmature circuit of the reel motor 'l and are booster eld 3l iscontrolled by an electro-responsive regulator shown generally at i3.

The regulator i3 has a main coil 23 which is energized from a shunt 6I(which may be the interpole winding or motor 1) in the armature circuitof motor 1 and which controls the iield 3l of the booster IE so as tomaintain the current in the armature of the motor 'l' at a constantvalue. In order to maintain a constant tension on the strip 5, the held33 of the motor 1 is controlled in accordance ith the relative change inspeeds of the machine 1 and the machine 3, which relative speed changeis a measure of reel diameter change. -l

Ii, for example, the strip material is being wound on the reel 3, thespeed of rnotoi 1 must decrease with reel build-up in order to maintaina constant tension on the strip i. The eld of the machine 1 iscontrolled by means of the difference in reference voltages of twotachometerI generators and I5 mechanically connected to the reel motor 1and the roll motor 9, respectively.

These tachometer generators I4 and I5 are pro-V vided with constantexcitation, such as permanent magnets (not shown) and the voltagesthereof measure the speeds of motors 1 and 3. A portion (which may be novoltage) of the voltage across generator I5 is connected in opposedseries rela.- tion with the voltage of generator I4 and in series withthe coil 34 of a polarized relay shown generally at IB. The polarizedrelay I6 when operated energizes a raise relay 53 or a lower relay 5Iwhich in turn controls a motor I1 operating a set of rheostats I8, Iland 2|. Y

Resistance l2 is utilized to reduce. the current in coll 34 when thearmature 35 has closed with contact 38 or 31. Resistance 42 is normallyshunted by a circuit including back contacts 4l and 4I of relays BI and53, which open upon energization of these relays. This reduction ofenergization permits armature 35 of relay I 6 to drop back to neutralposition upon little further reduction of the current in coil 34,although the air gap of relay I5 may have been reduced upon picking upof the armature.

Operation of the motor operated rheostat provides three distinctresults. The operation of motor I1 rst results in the varying of theamount of resistance i9 in circuit with the leld 28 or machine 1,thereby changing the excitation of motor 1 to maintain the voltageconstant althougl the speed is changed, thereby maintaining a constantpower output and constanttension on the strip 5. Tnesecond result of theoperation of the motor Il the variation of the setting of arm ZI therebyconnecting one cf fre resistances 25, 21, 28, 29 or series with theinertia compensation coil 2'2 of the regulator i3. This provides forvarying the amount ci' available inertia compene sation dependent uponthe amount of materiel on the reel E. The third result of operation ofthe motor I1 is the variation of that part of resistance IB, shuntedacross the tacliometer generator I5, which is in circuit with thetachometcr generator I4 and the coil 34 of the polarized relay I6, Thisaction changes the amount of reference voltage of the machine I5 so thata new balance of the relay 34 is obtained at the changed speed ci motor1.

For example, it may be considered that the strip material 5 is beingwound on the reel 6 and that the reel is about half ful?. of material.As the material built up on the reel, thetensicn in the strip 5increases momentarily which momentarily decreases the speed of motor 1andtherefore the voltage of the tachometer generator Il. This decreasein the voltage of generator II relative to the voltage of generator I5permits a current to flow through the coil 3l of the polarized relay I6in such direction as to move its armature 35 to close contact 35.Closing of contact 3i energizes relay 5I which closes its contact 3l torun the motor I1 in a clockwise direction as viewed in the drawing.

If the strip tension had decreased and hence the voltage of 'generatorIl had increased relative to the voltage of generator I5, armature 35would have closed with contact 31, thereby energizing relay 50 to closecontact 33 and run the motor I1 in a counterclockwise direction asviewed in the drawing.

Rotation of motor I1 in a clockwise direction decreases the amount ofresistance in circuit with the eld 2U of motor 1, thereby increasing theexcitation oI motor 1 until the voltage of the machine I4y is such thatthe desired tension is again obtained in the strip 5. This same movementof the motor I1 changes the setting ofthe potentiometer resistance I8thereby obtaining the new reference voltage value corresponding to thenew speed setting at which the voltages of Il and Il will balance. Atthe same time a new setting of the arm ZI is obtained by which theamount o! y power available for correct compensation of the regulator I3upon acceleration or deceleration is obtained.

By varying the potentiometer connection of the rheostat I8 to obtain anew balance after a speed change, a distinct advantage is obtained overprior art systems in which such new balance was obtained by varying theeld o! the generator I 5. No inaccuracies due to difference insaturation curves of machines I4, I5 are introduced due to the use ofthis potentiometer connection. A change in field strength of only onemachine tically no load conditions. Under such condi-` tions, a highresistance nlm builds up on the .commutators of these machines, whichresistance fluctuates greatly. In these prior art systems, no currentflows through the commutator when the generators are balanced and only avery small current when the generators are unbalanced suiiiciently toinitiate a regulating change. These very small currents are greatlyaffected by the v resistance fluctuations and hence cause considerableregulating inaccuracy. The inaccuracies in tension control resultingfrom such fluctuations are avoided in the present invention by having anappreciable load current flow through machines I4 and I5 at all times.

As the ratio of reel diameter to reel speed at any constant strip speedis not a linear function and as the ratio of terminal volts of generatorIl to reel speed is a linear function, one of the resistances I8 or I9vmust be stepped non-linearly in order to have the position of the motoroperated rheostat shaft-32 a measure of reel diameter. This can beeffected by stepping resistance I9 in equal R.. P. M. per step andsteppingresistance I8 in steps in accordance with the speed-reeldiameter curve of generator I4. This can also be effected by steppingresistance 'I9 in steps in accordance with Athe reel diameter-reel speedcurve and stepping resistance I8 in equal volts per step.

It will be noted, assuming that the strip is being wound on the reel 6,that the-speed of motor 1 must decrease in proportion to the change inreel diameter of the reeled material in order to maintain the desiredtension. This means, in effect, that the rotation of the shaft 32operated by the motor I1 will be in proportion to the change in reeldiameter and therefore the position of shaft 32 is a measure of the reeldiameter. The function of the rheostat 2I is therefore to modify thecontrol effected ,by the regulator i3 in accordance with the actualdiameter of reeled materia15. This provides that the compensation of theregulator I3 during acceleration or deceleration is further modifieddependent upon the amount of strip material 5 on the reel 6 at the timeof such acceleration or deceleration.

Although shown in connection with this particular tensioning controlsystem, this compensation feature is applicable to any control systemutilizing inertia compensation and provided with an element measuringreel diameter change. In the particular control system shown anddescribed, reference has been made to the desired tension. This tensionmay be maintained at a constant value or may be progressively increasedor decreased or may have any predetermined sequence of values. Thedesired tension may be obtained in various ways by controlling the powertransmitted between the reel S and the dynamoelectric machine l.Broadly, this is doneby maintainingy one or more of the variouscharacteristics of operation, such as current, voltage, torque, speedand the like, in accordance with predetermined sequences of values.

The positions of the tap points on the resistors to lll are determinedby means oi curves such as shown in Fig. 2. These curves are plottedfrom actual design figures of the specific mill on which this controlsystem is to be used and show the percentage full load acceleratingcurrent necessary toaccelerate or decelerate the mill at various reeldiameters (amount of strip material onthe reel 6) for various widths ofthe strip 5.

For example, the left hand taps of the five resistors 26 to 30correspond to points on the lowest curve of Fig. 2. Thus, if the handwheel 25 is set s that each rheostat arm is in the lowermost positionshown, the compensation available is that designed for the narroweststrip to be'run.

If a wider strip is to be rolled, the hand wheel 25.

is set in the position shown in the drawing. If a still wider strip isto be rolled, the hand wheel is rotated in a clockwise direction and setat the proper setting for such strip width. The number of settings isdetermined by the number of widths to be rolled. The setting of thishand wheel is made prior to the rolling of the strip and only onesetting' is necessary for the entire rolling at that strip width.

The setting of the hand Wheel 25 in accordance with the strip width maybe effected automatically in any suitable manner, for example, as bymeans of photoelectric relays operated by interception of a light beamby the strip.

The need for variation in the amount of acceleration -and decelerationcompensation, in order to accurately maintain the desired tension, isevident when the variation of the factors a'ffecting thelnertia of Athereel is considered. In 1 entry reel is always empty but the deliveryreel may have varying amounts of strip thereon.

A strip rolling mill may at times be accelerated and decelerated otherthan at the beginning and end of the pass. For example, when coils aresticky or have cracked edges, the operator usually decelerates the millto a comparative low speed, usually about fty percent of full speed,until the bad sections are rolled and then again accelerates the mill tofull speed. Obviously, for a control system to accurately supply thecompensation necessary for acceleration or deceleration, a measure ofthe varying values of the reel inertia must be had.

When the material is all reeled onto the reel 6 and the reel 6 isremoved from the mill, a switch 45 is actuated to closed position. Themeans for operating this switch 45 by removal of the reel 6 is not shownin the schematic diagram, but may be by any suitable means such as thecoil stripper, which usually includes a hydraulic piston utilized topush the coil of strip material off the reel. Closure of this switch "l5energizes a limit relay which closes its sealing contacts t3 and alsocloses its contacts til which energize the motor il to run it back toits previous position. A limit switch 46, 4l, 43 interrupts the circuitto the limit relay when the rheostat il is returned to its beginningposition.

The specific showing in the drawing oi' the polarized relay I3 in serieswith the generator it and a variable part of resistor lil is thepreferred embodiment. Broadly, it is necessary to have the relay itresponsive to the difference between the voltages or the generators itand i5, one of which voltages is modified in accordance with reeldiameter change. Either of the two voltages may be so modified. Suchmodification of the voltage of generator l5 will decrease its effectivevoltage in accordance with reel build-up. Such modification of theeffective voltage of generator Il will increase its effective voltage inaccordance wit the reel build-up.

As shown in Fig. 3, a double coil relay I6' may be similarly utilized tocontrol contacts 36 and 3l. This relay I6 has opposed coils 63 and ilwhich when equally energized maintain the armature 35 in the neutralposition shown. Coil 64 measures the voltage of generator Il and coil 63measures the effective voltage of generator I5 as modified by a variableresistance i8' controlled by the shaft 32 of the motor operated rheostatil. The operation of contacts 36 and 3l relative to the differencebetween the voltages of the generators i4 and l5 is similar to theiroperation in the embodiment shown in -Fig. 1

Any reelable material, such as steel strip, Wire, metal foil, textiles,paper or similarmaterial, may be tensioned by the control system of thisinvention.

Although but one embodiment of the present invention has beenillustrated and described, it will be apparent to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims.

It is claimed and desired to secure by Letters Patent:

l. In combination, a dynamo-electric machine, a device subject tovariations in its moment of inertia, a power transmitting connectionbetween said device and said dynamo-electric machine, means for normallymaintaining the power transmitted between said dynamoelectric machineand said device at a substantially constant value, means for changingsaid value of transmitted power during a period of acceleration ordeceleration, and means including an electroresponsive device forpredetermining said change in said value in accordance with variationsin the moment of inertia of said device.

2; In combination, a dynamo-electric machine, a reel for strip material,a power transmitting connection between said reel and saiddynamoelectric machine, means for normally maintaining the powertransmitted between said dynamoelectric machine and said reel at asubstantially constant value, means for changing said value oftransmitted power during a period of 'acceleration or deceleration, andmeans including an electroresponsive device for predetermining .saidchange in said value in accordance with the amount of said stripmaterial on said reel.

3. In combination, a dynamo-electric machine, a reel for strip material,a. power transmitting connection between said reel and saiddynamoelectric machine, means for normally maintaining the powertransmitted between said dynamoelectric machine and said reel at asubstantially constant value, means for changing said value oitransmitted power during a period of acceleration or deceleration, andmeans including an electroresponsive device for predete ning said changein said value accordance an.; the width of said strip material.

Q In combination, s, dynamo-electric machine, a reel for strip material,a power transmitting connection between said reel and sm'ddynamoelectric machine, means for normally maintaining 2,see,14e

the power transmitted between said dynamoelectric machine and said reelat a substantially constant value, means for changing said value oftransmitted power during a period of acceleration or deceleration, andmeans including an electroresponsive device for predetermining saidchange in said value in accordance with the reel diameter of said stripmaterial on said reel.

5. In a control system, a dynamo-electric machine, a material carryingreel, a power transmitting connection between said reel and saiddynamo-electric machine, means for performing an operation on saidmaterial, and means for controlling said dynamo-electric machine tomaintain a predetermined tension on said material while being wound uponor unwound from said reel, said controlling means comprising a firstconstant excitation generator connected to said dynamo-electric machineso that the voltage of said first generator varies in accordance withthe speed of said dynamo-electric machine, said controlling meansfurther comprising a second constant excitation generator connected tosaid operation performing means so that the voltage of said secondgenerator varies in accordance with the speed of said operationperforming means, and said controlling means further comprising meansselectively controlling said dynamoelectric machine in response to thedirection of a difference of the voltages of said generators.

6. In a control system, a dynamo-electric machine, a material carryingreel, a power transmitting connection between said reel and saiddynamo-electric machine, means for performing an operation on saidmaterial, means for' controlling said dynamo-electric machine tomaintain a predetermined tension on said material while being wound uponor unwound from said reel, said controlling means comprising a firstgenerator connected to said dynamo-electric machine so that the voltageof said first generator varies in nccordance with the speed of saiddynamo-electric machine, said controlling means further comprising asecond generator connected to said operation performing means so thatthe voltage of said second generator varies in accordance with the speedof said operation performing means, said -controlling means furthercomprising means responsive to a difference of the voltages of saidgenerators, and means providing said generators with a substantial loadcurrent when said voltages thereof are substantially equal.

'l'. In a control system, a dynamo-electric machine, a material carryingreel, a power transmitting connection between said reel and saiddynamo-electric machine, means for performing an operation on saidmaterial while being wound upon or unwound from said reel, a firstgenerator connected to said dynamo-electric machine so that the voltageof said first generator varies in accordance with the speed of saiddynamo-electric machine, a second generator connected w said operationperforming means so that the voltage of said second generator varies inaccordance with the speed of said operation performing in response tooperation oi' said electroresponsive device for controlling theenergization of said dynamo-electric machine and for varying said tappedconnection.

8. In a control system, a dynamo-electric machine, a material carryingreel, a power transmitting connection between said reel and saiddynamo-electric machine, means for performing an operation on saidmaterial while being wound y upon or unwound from said reel, a ilrstgenerator connected to said dynamo-electric machine so that the voltageof said first generator varies in "vice operatively responsive to thedifference between said variable part of the total voltage across saidresistance means and the voltage of the other of said generators, meansincluding an electro-responsive element for varying the energization ofsaid' dynamo-electric machine during acceleration and deceleration ofsaid ree1, and means operative in response to. .operation of saidelectroresponsive device for controlling the energization of saiddynamo-electric machine, for varying said tapped connection, and forvarying the operativeeil'ect of said electroresponsive element. i

9. In a control system, a dynamo-electric machine, a ree1 carrying stripmaterial, a power transmitting connection between said ree1 and saiddynamo-electric machine, means for performing an operation on saidstrip, means for controlling said dynamo-electric machine for normallymaintaining the power transmitted between said dynamo-electric machineand said reel at a substantially constant value to thereby maintain apredetermined tensionon said material between said reel and saidoperation performing means, means for changing said value of transmittedpower during a period of acceleration or deceleration to therebymaintain said predetermined tension on said material, and meansincluding an electroresponsive device for predetermining said change insaid value in accordance with variations in the moment of inertia ofsaid reel and said material thereon.

l0. In a control system, a dynamo-electric machine, a reel carryingstrip material, a power transmitting connection between said ree1 andsaid dynamo-electric machine, means including a current regulator forcontrolling said dynamoelectric machine for maintaining the powertransmitted between said dynamo-electric machine and said reel at asubstantially constant4 value at constant strip speed, means forchanging the speed of said strip, means comprising a biasn ing means forsaid current regulator for changing said value of transmitted powerduring said speed changing, and means including an electrom responsivedevice for predetermining said regulator bias in accordance with themoment of inertia oi said ree1 and the strip material thereon.

11. In a control system, a dynamo-electric machine, a reel carryingstrip material, a power transmitting connection between said reel andsaid dynamo-electric machine, means including a current regulator forcontrolling said dynamoelectric machine for maintaining the powertransmitted between said dynamo-electric machine and said reel at asubstantially constant value at constant strip speed, means for chang-ving the speed of said strip, means comprising a biasing means for saidcurrent regulator for changing said value of transmitted power duringsaid speed changing, and means comprising a resistor the value of whichis preset in accordance with the width and reel diameter of said reeledmaterial for predetermining said regulator bias.

12. In a control system, a dynamo-electric'machine, a material carryingreel, a power transmitting connection between said reel and saiddynamo-electric machine, means for performing an operation on saidmaterial, means for maintaining a constant tension in said materialbetween said reel'and said operation performing means, for anypredetermined speed of said operation performing means, said tensionmaintaining meanscomprising meansfor maintaining the armature current insaid dynamo-electric machine at a constant value except duringacceleration and deceleration of said dynamo-electric machine, saidtension maintaining means further .comprising means for modifying saidcurrent controlling means to vary said armaturev current duringacceleration and deceleration of said dynamo-electric machine, and saidtension maintaining means further comprising means operative inaccordance with a change in ree1 diameter of said material forcontrolling the excitation of said dynamo-electric machine and forvarying the operative eil'ect of said modifying means.

13. In a control system, a dynamo-electric machine, a material carryingree1, a power transmitting connection between said reel and saiddynamo-electric machine, means for performing an operation on saidmaterial, means for maintaining a predetermined tension in said materialbetween said reel and said operation performing means, for anypredetermined speed of said operation performing means, said tensionmaintaining means comprising means for maintaining the armature currentin said dynamo-electric machine at predetermined values except duringacceleration and deceleration of said dynamoelectric machine, saidtension maintaining means further comprising means for modifying saidcurrent controlling means to vary said values of armature current duringacceleration and deceleration of said dynamo-electric machine, and saidtension maintaining means further comprising means operative inaccordance with a change in reel diameter of said material for coni.trolling the energization of said dynamo-electric

